As shown in FIG. 1, a two-layer cover umbrella is popular for releasing wind pressure by use of the space between two covers. This two-layer cover umbrella can then prevent the frame from damage by strong wind. The conventional structure usually includes a branch rib (1), which has inner end a connector (11) as shown in FIG. 2 to 4. A rivet (12) is used to joint the connector (11) with a primary rib (2). Hence, the branch rib (1) is capable of connecting the upper cover. A drawback of this umbrella is that the connecting strength between the branch rib (1) and the primary rib (2) is weak. If strong wind occurs, the branch rib (1) will be still broken. Further, the connector (11) is obviously projected as a step from the primary rib (2). The upper cover will be easily broken and the outlook of the umbrella is not good.
The present invention is to provide an improved rib structure for using in a two-layer cover umbrella, which can solve the problem of the prior art and obtains improvement and utilization. Now, accompanying with the following drawings, the character of the present invention will be described here and after.